The first strain of T. equigenitalis was isolated by Crowhurst, 1977, Vet. Rec. 100, 476 and characterized by Taylor et al., 1978, Equine Vet. J. 10, 136-134. This bacterium is the agent of a venereal disease of the Equidae called contagious equine metritis (designated CEM hereinafter).
Since the first appearance of this disease in 1977 at Newmarket (Great Britain), CEM has spread among the world's equine population (Europe, USA, Japan).
CEM was initially characterized by the appearance of purulent vaginal discharges caused by acute endometritis. The epidemiology and the clinical signs of the disease have now changed. Very few foci remain, exhibiting an acute form of CEM; it is then a question of contamination of several mares in the same harem. Clinical forms of metritis have in fact become rare, and T. equigenitalis is mainly found in asymptomatic carriers or at the preclinical stage. The disease is transmitted by stallions that do not show any clinical symptom.
CEM constitutes an obstacle to the international exchange of Equidae and its screening is recommended by the IEO (International Office of Epizootics), list B).
Indirect screening means such as serology have been abandoned by numerous countries such as the USA, Great Britain and France.
Direct screening means are implemented: screening by bacteriological culture in numerous countries, screening by indirect immunofluorescence.
In France, prophylactic measures comprise both bacteriological culture and indirect immunofluorescence (IIF).
Systematic screening of stallions has become mandatory prior to each mating season.
For economic and management reasons, this systematic screening can only be done from one or two samples per animal and per season. The reliability of this screening is therefore even more crucial.
The screening test for infection by T. equigenitalis currently employed in France is based mainly on isolation of the bacterium by culture on nutrient and/or selective media and on the identification of this agent according to morphologic and biochemical criteria. However, T. equigenitalis is a very fragile and very slow-growing bacterium (the observation time of the culture dishes is at least 6 days). Furthermore, it is liable to be inhibited by other bacteria of the flora examined. The criteria for identifying the various strains of T. equigenitalis are themselves either too succinct and liable to variations (demonstration of absence of activity for the three classical enzymatic activities exhibited by T. equigenitalis), or too extensive to be managed in the required time. Detection by the bacteriologic technique alone has therefore become a hazardous method of diagnosis. An indefinite percentage of healthy carriers is thus regarded as uninfected each season.
A second test for detecting infection by T. equigenitalis has been adopted in France. This test is based on identification of the bacterium by indirect immunofluorescence using antiserum made in the rabbit and fluorescent anti-rabbit antibodies. This assay has the advantage that it delivers its results much more quickly (24 to 48 hours) than an assay by bacteriologic culture.
Application of this technique can, however, lead to errors through excess (false positives), as in many cases the antisera used give rise to reactions with species other than T. equigenitalis. 
The significance of these results is thus very limited: if the immunofluorescence assay is negative, the registered laboratory may report a negative conclusion, but if the result is positive, this result must be either confirmed or invalidated by bacteriology.
The inventors tried to rectify these difficulties in the detection of infection by T. equigenitalis, by elaborating new means for identifying a bacterium of the species T. equigenitalis without risk of false positives or of false negatives. The present invention also offers advantages of speed and simplicity of execution.